Various means have been devised to simplify the adjustment of axle bearings, specifically, truck axle bearings. It is generally accepted that in some bearing installations, for example, axle bearings, the life of the bearing will be optimized if the adjustment is made for a slight axial compressive deflection, for example, about 0.003 inches (where this amount is the compressive deflection of the two bearings combined), which is often referred to as “a three thousandths preload.” Typical prior art methods of creating these preloads are obtained by applying specified torques to the bearing assembly, for example, by tightening the nut that retains the bearings. However, for several reasons, it is typically extremely difficult to achieve such preload settings under actual in-field conditions, as in a mechanic shop. For example, the assembly of a heavy truck wheel onto a wheel hub assembly is a relatively cumbersome procedure that hinders the mechanic. Moreover, the wheel hub assembly always includes at least one inner seal, usually a lip type of seal, which can impose a resistive drag torque component to the preload torque, particularly when the seal is new.
One of the popular means of adjusting bearing preload by means of an applied torque is described in the literature provided by the Stemco Company, of Longview, Tex. (for example, Stemco form 571-2970) and further in instructions provided by Stemco (for example, Stemco part number 09-571-0006). These instructions are typically packaged with Stemco's axle spindle nuts. The accuracy of this and other prior art preloading methods is limited because they rely on the relationship between assembly torque and axial preload of the bearings, which will vary with variations in torsional resistance or friction of the nut against the face of the bearing, and will also vary with variations in torsional resistance or friction of the nut against the spindle thread, the nut against the bearing face, and the aforementioned lip seal present in the assembly.
Due to the limitations and disadvantages of these and other prior art bearing preloading methods and devices, there is a need to provide accurate and repeatable procedures and devices for providing and adjusting bearing preload. Aspects of the present invention overcome the limitations and disadvantages of the prior art and provide methods and apparatus for creating known, monitorable, uniform preload that is not subject to the inaccuracies of prior art methods and devices. Moreover, aspects of the present invention are easier to apply by a mechanic.